New Study on Nerve Block for Back Pain
To understand the importance of a new research paper, you should know that the vertebral bones of the spine have several important functions. They must protect the spinal cord, support the head and upper body, and enable egress of nerves that carry sensation and control muscles. They also need to remain flexible enough to allow freedom of movement. To accomplish all this, the vertebra has a complex yet marvelously esthetic structure that includes two wing-like bones called facets. They connect to the main vertebra via a small joint.
Connected to this joint is the medial branch nerve that allows you to feel pain from the joint but does not control muscles or carry sensation from elsewhere. This makes it a good target for treatment of back pain because blocking the nerve won’t affect muscle function or skin sensation.
There are several different ways to block this nerve. Three were used in the study.
A temporary nerve block with a local anesthetic (see drawing) as a test. If the nerve block relieves the pain, then that suggests (but doesn’t prove) the medial branch nerve is responsible for the pain. The effect of the block lasts only for a few hours.
Freezing the nerve (cryoneurolysis) to cause temporary nerve destruction that permits the nerve to grow back over weeks to months.
Heating the nerve with radio waves (radio frequency ablation or RF) to cause temporary destruction that lasts six to eighteen months.
The researchers (from Denmark) selected 120 patients who had at least 50% pain relief an hour after a block with local anesthetic. This implied they would be likely to improve after the other treatments. They were then divided into three groups of 40 patients and given either cryoneurolysis, RF, or a placebo.
Four weeks later the patients were given a survey called the Patient Global Impression of Change. They also were assessed for pain intensity, quality of life, disability, depression, and catastrophizing at 4 weeks, 3, 6 and 12 months.
Results: There were no differences between the three groups on these measures. Neither the cryoneurolysis nor the RF were better than the placebo.
These results mean:
Pain relief was due to the placebo effect and not the nerve block.
The patients’ pain was not from the medial branch nerve since the results were the same whether you blocked the nerve (cryoneurolysis or RF) or not (placebo).
Treatment of the medial branch nerve therefore has no place in back pain management.
This study is consistent with many others about a range of clinical conditions (see our Bibliography) showing that invasive treatment for chronic pain (as in this study) or non-invasive non-psychological treatment has no more than placebo benefit. When this evidence is seen in the context of dramatic benefits for chronic pain from the psychophysiologic approach (much better than placebo in many recent studies) it is clearly time for a major shift away from prevailing invasive or non-psychological practices.
Truong K, Meier K, Ahrens LC, et al
Cryoneurolysis versus radiofrequency ablation outcome on pain experience in chronic low back pain (COPE): a single-blinded randomised controlled trial.
RMD Open 2024;10:e004196. doi: 10.1136/rmdopen-2024-004196
https://rmdopen.bmj.com/content/10/2/e004196
